Proposed Specifications for Nutria-Resistant Geotextiles, by Dr. Adrian Lawler

Proposed Specifications for Nutria-Resistant Geotextiles

by Dr. Adrian Lawler
(retired) Aquarium Supervisor (l984-l998) J. L. Scott Aquarium Biloxi, Ms 39530

Original to Aquarticles

Nutria , Myocastor coypus, are highly destructive plant-eating rodents found in many areas of the world mostly in temperate watery environments. Their digging actions to obtain food and to make burrows lead to extensive loss of soil, loss of land elevation, expansion of water-inundated areas, and other problems for wet environments and the organisms living there (see Lawler, 2006, Nutria: Trouble for waterways, http://www.aquarticles.com/articles/ponds/Lawler_Nutria.html ). They were no doubt a contributing factor in levee failure in the New Orleans area during Hurricane Katrina in 2005. They have caused severe soil loss on my farm on Weeks Bayou near the coast of Mississippi, and I have been trying different means of control for many years. Previously I used small mesh fencing wire to exclude nutria from bayou and pond banks, but this rusts away; recently I have been researching geotextiles, etc.

Geotextiles are permeable fabrics used on/in soil that separate, filter, reinforce, protect, or drain (http://en.wikipedia.org/wiki/Geotextile). They are widely used in many types of applications and have important use on/in banks of watery environments for erosion control, land building, bank/levee protection against storms and rodents, etc.

Internet searching has yet to reveal a suitable nutria-proof geotextile. For this reason I am submitting my list of generalized specifications for nutria-resistant/excluding geotextile to the public domain in hopes that a manufacturer can solve this problem and present the world with an affordable way to limit nutria damage to levees and waterway banks around the world, thus helping save marshes, ponds for aquaculture and tropical fish rearing, levee-protected cities, and various other lands. Such a fabric could also serve in retaining soil and sand in island and land-building construction, in storms and floods, and in erosion control.

Following is a list of proposed generalized specifications that I propose to be met in order to design, manufacture, and install a nutria-resistant barrier fabric, or geotextile. These specifications were previously sent to a geotextile manufacturing company that had contacted me about nutria biology and possible ways for testing a geotextile they were developing for nutria resistance/exclusion. I decided to release my thoughts about nutria-resistant geotextile specifications to the public domain for the potential use by anyone, in case such ideas might help such geotextile development.

PHYSICAL CHARACTERISTICS

---Permeable to permit water flow through fabric (so levee, bank, etc. maintains normal moisture content to prevent compaction and loss of levee height; and water flow can maintain plant life on levee/bank and beyond).

---Should allow grass or sod to grow on top or through fabric (root or shoot penetration of fabric to help anchor geotextile).

---Should have alternate product with larger openings in fabric to allow for larger marsh plant roots to pass through fabric to anchor fabric. This alternate product would be used in marsh areas, etc., where lawn-type grass does not grow.

---Resistant to penetration, tearing, etc. by floating logs, debris, and ice moving downstream or pushed by storms.

---Resistant to damage by boats that hit bank where it is installed.

---Resistant to cutting with a knife, or any other common means of vandalism, while in storage, in transit, or after installed.

---Strong enough to prevent digging through fabric by rodents as large as nutria, and by armadillo (Tensile strength must be high enough to withstand nutria digging).

---Must not be easy for nutria to grab with teeth, and must withstand sharp bites or cuts.

---Resistant to, and unaffected by insects.

---Stay flexible and intact from 0 to 212 F at least. I would recommend heat resistance be high enough so that brush/grass fires above it do not damage buried fabric, either by heating the soil or by heating moisture in the soil.

---Must not melt under heat below 212 F, or readily burn.

---Must be flexible enough to conform to contours of banks (below and above water level) of water bodies.

---Must not become too brittle when frozen so it breaks apart under impact (from boats, ice, logs, debris, etc).

---Must not stretch (or have structures that move aside) to allow destructive rodents (nutria, in this case) to squeeze through any part of fabric structure.

---Must not be scoured away by abrasion from sand during wave action, or come apart during storm action. (Fabric should also serve as a storm erosion barrier.)

---Must not be badly compressed, or weakened, when riprap placed on top of it, or vehicles driven on it.

---Must retain soil and sand (not let soil and sand be washed out from behind fabric) so that it is of use in island/marsh building, bank stabilization, and erosion control.

---Top side must not be so slick that dirt slides off into water during rains and with flowing water, leaving geotextile exposed, or in any way makes bank less stable.

---Must not float up; should be more dense than water so it sinks (for ease of anchoring underwater, and for tightness of fit around underwater bank, and to stop any tendency to "float up" while buried which might disrupt levee stability when levee saturated with water).

---Can be easily patched (or overlaid and sealed) if damaged by severe impact, storm, fire, or vandalism.

---Must not have projections or sharp parts on top side, including anchors used, that could injure anyone walking on it, or falling down on it, etc. that could lead to lawsuits.

CHEMICAL CHARACTERISTICS

---Must be resistant to low pH, as in acid soils.

---Must be unaffected by salt or fresh waters, and compounds normally dissolved therein.

---Must be stable and not change physically or chemically over time.

---Must not break down over ______ years ( = specification of buyer).

---Must be inert and not react with anything in environment when buried, so its properties remain constant.

---Must not leach toxins of any sort into water or soil that could be taken up by plants or animals.

---Must be resistant to oil, diesel fuel, gasoline, alcohol, etc. that may be spilled in water, or drained into soil where buried.

---Must be UV light resistant so if geotextile is exposed (sod or dirt washed away by storms, floods, etc.) or installed on top of soil it will not break down in sunlight, or become brittle.

---Must not rust, decompose or rot, or break down in any way.

---Must not have organic content that supports fungi growth, or attracts insects.

INSTALLATION PROCEDURES

---** IF buried, should NOT be buried so deep as to cause most of grass root system to be ABOVE fabric and thus STILL available to nutria as food and thus lead to digging and eating of grass roots ABOVE fabric, unless the levee board plan is to sacrifice the top layer of grass roots to nutria digging but NOT ALLOW further levee penetration (past the geotextile).

---Site for installation should be cleared of rocks, wood, and debris prior to laying fabric.

---Fabric anchored so not washed away, or washed out of position on bank, by floods, wave action, or storms.

---Must be able to be anchored up to 4 feet below mean low water to prevent underwater nutria burrow entrance building.

---Must be easily adapted to fit/and be sealed around drainage pipes, pipelines, pier pilings, bridges, underwater structures and contours, etc.

---Must be securely joined together at end of each roll so final product becomes one continuous unit.

---Fabric should be rolled on or laid in the direction of the water flow, with overlaps of a foot (if not sealed) on top as go downstream, or in direction of prevailing current.

---Must be packaged in rolls light enough so can be installed manually in remote areas, i. e, don't have to bring in heavy equipment to move rolls. Can make longer rolls for heavy equipment installation, and shorter rolls for manual installation.

---Must be relatively easy to install, so people in less-developed areas can understand its installation procedures.

---Fabric should be thoroughly inspected for proper installation prior to adding soil, sod, or riprap on top.

MANUFACTURING

---Made in roll wide enough (10-20 feet) to protect bank at least 4 feet down under water and at least 6 feet above water level in ONE PASS, i.e., no overlapping , which means less future repairs needed. (overlapping presents a horizontal seam/flap that can lead to the top run of fabric being displaced by wave, storm, or flood action, requiring repairs.)

---If cannot be made in a wide roll for one pass, figure out way to seal geotextile at overlaps.

---Must be affordable (cost less, or last longer, than concrete, bulkheading, riprap, or fencing used to exclude nutria).

---Must have anchors/staples available to be sold with fabric. Such anchors/staples must be rust-resistant and last _____ years ( = specification of buyer).

---Must be free of oils, solvents, etc. from manufacturing process that might contaminate environment.

---Should be packaged so fabric does not get contaminated by toxins while in storage or transit, or by vandalism.

---Can have top layer of a coarser fabric to retard nutria, and bottom layer made of finer fabric to retain sand.

It is not known if a geotextile manufacturing company can presently manufacture an affordable product that will exclude nutria from waterway banks. After research it may be found that geogrids are more suitable for nutria exclusion. A HDPE-coated wire mesh fencing (geogrid) may last longer than the wire fencing I previously used. It may also be found that a geogrid and a geotextile can combined to make a fabric that will both exclude nutria and protect banks from erosion.

Author Information must remain with article.